I think you are confusing user interface design with user experience (UX). A text-book UI should be intuitive and easy to use, but that doesn't necessarily mean it will be aesthetically pleasing to everyone. I work with UX, and one of the biggest challeges i face is to find a good balance between functionality and aesthetics; what will give the general user base the best possible experience.

But you have to realize that it is impossible to satisfy everyone, especially when looking at OSX-users and Windows-users, who have such different tastes and demands. Then its probably better to have two different UIs that can bring a great (but not necessarily the same) user experience to two very different crowds.